Preparation of sulfonic acid containing fluorocarbon vinyl ethers

ABSTRACT

VINYL ETHERS OF THE FORMULA CF2=CFOCF2CFXSO3ME, WHEREIN X IS F OR CF3 AND ME IS ALKALI METAL, ARE MADE BY CONTACTING AND REACTING AN ALKALI METAL ALKOXIDE WITH A COMPOUND OF THE FORMULA   2-(CF3-),2,4,5,5-TETRA(F-),4-X-1,3-OXATHIOLANE 3,3-   DIOXIDE   IN AN INERT ORGANIC SOLVENT. THE VINYL ETHER REACTION PRODUCTS CAN BE COPOLYMERIZED WITH FLUOROCARBON MONOMERS, E.G., TETRAFLUOROETHYLENE, TO FORM IONICALLY CONDUCTIVE MATERIAL FOR USE AS FUEL CELL MEMBRANES.

United States Patent 01 Ffice 3,560,568 PREPARATION OF SULFONIC ACIDCONTAINING FLUOROCARBON VINYL ETHERS Paul Raphael Resnick, Wilmington,Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del.No Drawing. Filed Nov. 26, 1968, Ser. No. 779,235

Int. Cl. C07c 143/16 U.S. Cl. 260-513 1 Claim ABSTRACT OF THE DISCLOSUREVinyl ethers of the formula CF =CFOCF CFXSO Me, wherein X is F or CF andMe is alkali metal, are made by contacting and reacting an alkali metalalkoxide with a compound of the formula in an inert organic solvent. Thevinyl ether reaction products can be copolymerized with fluorocarbonmonomers, e.g., tetrafluoroethylene, to form ionically conductivematerial for use as fuel cell membranes.

This invention relates to a process for preparing certainsulfonyl-containing fluorocarbon vinyl ethers.

Sulfonyl-containing fluorocarbon vinyl ethers having the formula FSOCFR,CF O(CFXCF O),,CF=CF wherein Rf is F or perfluoroalkyl, X is F or CFand n is to 12 are disclosed in U.S. Pat. No. 3,301,893 to Putnam et al.as being prepared by pyrolyzing the salt FSO CFR CF O(CFXCF O) CFCFOOONa, wherein Rf, X and n have the same meanings as indicated above.

It has now been discovered that certain sulfonyl-containing fluorocarbonvinyl ethers can be obtained by contacting and reacting an alkali metalalkoxide with a cyclic sulfone of the formula wherein X is F or 0P in aninert organic liquid which is a solvent for the sulfone. The resultantvinyl ether salts have the formula CF =CFOCF CFXSO Me, wherein X has theabove-indicated meaning and Me is the alkali metal of the alkoxide.

The vinyl ether salts can be converted to the corresponding sulfonylchloride (SO Cl) by reaction with P01 and in turn to the correspondingsulfonyl fluoride (-SO F) by reaction of the sulfonyl chloride with NaF.The vinyl ether salts can be converted to the corresponding sulfonicacid (-SO H) by reaction with a strong inorganic acid such as H SO Thesevinyl ethers can be used in the same manner as the vinyl ethersdisclosed in U.S. Pat. No. 3,282,875, to Connolly et a1. As disclosedtherein, the conversion reactions, i.e., salt to halide, acid, or otherderivative, can be practiced on polymer containing repeat units derivedfrom the vinyl ether. Copolymers containing the sulfonic acid form ofthe vinyl monomer prepared herein can be used as ionically conductivemembranes in such applications as fuel cells and batteries as disclosedin U.S. patent application Ser. No. 639,515, filed May 18, 1967, byWolfe and now abandoned.

The process of the present invention is conducted merely by adding thealkoxide and cyclic sulfone to the inert organic solvent in aboutequimolar quantities conveniently at ambient temperatures, but higher orlower temperatures such as from -20 to 200 C. can be used. The reactioncan also be conducted at atmospheric pressure, although higher or lowerpressures can be used.

3,560,568 Patented Feb. 2, 1971 Suitable solvents include those whichare free of Zerewitinoff active hydrogen atoms. Thus, the solvent shouldalso be anhydrous. Examples of suitable solvents include benzene andsubstituted benzene such as chlorobenzene, nitrobenzene, ethers such asdiethyl ether and diphenyl ether, and cyclic ethers such astetrahydrofuran. Suflicient solvent is used to dissolve the amount ofsulfone reactant that is present.

The alkoxide reactant can be represented by the formula ROMe wherein Meis any alkali metal, preferably Na or K, and R is any hydrocarbon groupwhich does not interfere with the reaction.

The alkoxide reactant need not be soluble in the particular solventused. Examples of suitable alkoxides include sodium methoxide, potassiummethoxide, cesium methoxide, lithium methoxide, rubidium methoxide,sodium ethoxide, potassium butoxide, and sodium phen oxide.

The cyclic sulfone reactant can be made by pyrolyzing at a temperatureof from 200 to 600 C. in contact with a dry alkali metal salt such as NaCO a compound of the formula FSO CFXCF O'CFCF COF, wherein X if F or01%, which is disclosed in U.S. Pat. No. 3,301,893 to Putnam et al.

The following examples are intended to illustrate the present inventionand not as a limitation on the scope thereof. Parts and percents are byweight unless otherwise indicated.

EXAMPLE 1 To a three-necked, two-liter flask fitted with a droppingfunnel, mechanical stirrer, thermometer, still, receiver and Dry-Icecooled trap is added 240 g. (2.25 mole) anhydrous Na CO dried in a fluidbed under nitrogen. The entire apparatus is flamed out in a stream ofdry nitrogen and the sodium carbonate in the flask heated to 300. Theflask is cooled and 750 ml. of anhydrous diethylene glycol diethyl ether(diglyme) is added through a silica gel column. 519 g. of

FSOzCFzCFzOCFCOF is added slowly, over a three-hour period, and theevolution of carbon dioxide is monitored with a bubble-flow indicator.The mixture is stirred until evolution of CO stops and is then heated toremove the distillate boiling up to The material in the receiver andtrap is greater than 99 percent cyclic sulfone of the formula CF3CFSOGF2O-CF To a magnetically stirred 500 ml. three-necked flask, fitted with awater-cooled reflux condenser, pressure-equalizing dropping funnel anddrying tube, is added 20.8 g. sodium methoxide (0.386 mole) and 300 g.of anhydrous ether. 112 g. (0.40 mole) of the cyclic sulfone prepared inthe previous paragraph is added slowly through the dropping funnel andthe mixture stirred at room temperature overnight. When the solution isclear, the ether is stripped off on a rotary evaporator and theremaining white salt having the formula CF =CFgOCF OF SO Na is dried ina vacuum oven at 60 for 24 hours.

A 350 ml. stainless steel cylinder is charged with ml. of distilledwater, 0.75 g. ammonium carbonate, 0.30 g. ammonium persulfate and 10 g.of the vinyl ether prepared in the previous paragraph. The mixture isheated to 70 and the cylinder pressured to 300 p.s.i. withtetrafiuoroethylene. At the end of 5 hours the mixture is cooled and awhite solid polymer recovered. The polymer is washed twice with water ina blender and dried in vacuum at 60. The product, 19.3 g., has a M.P 12lower than that of polytetrafluoroethylene and its DTA shows the absenceof some phase changes normally present in polytetrafluoroethylene. An IRspectrum of the copolymer shows the presence of bands due to the vinylether comonomer.

EXAMPLE 2 To a 200 ml. flask fitted with a magnetic stirrer and smallstill are added 30 g. of the vinyl ether of Example 1, and 42 g.phosphorous pentachloride. This is heated slowly and a colorlessdistillate (B.P. ca. 105 of 28 ml. is obtained, which is a mixture ofmainly POCl and CF =CFOCF CF SO CL A 200 ml. three-necked flask isfitted with a magnetic stirrer, thermometer, still and dropping funnel.The flask is charged with 50 g. of sodium fluoride and 50 g. oftetramethylene sulfone and heated to 100. The crude CF =CFOCF CF SO Clproduct described above is added slowly and the material boiling at 70collected. Gas chromatographic and IR analysis show the presence of amajor proportion of this to be CF =CFOC=F CF SO R This is chlorinated ina sealed carius tube with chlorine to give CFQCI-CFClOCF CF SO- F, whosestructure was consistent with the observed NMR, IR and mass spectralanalyses.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that this CFaCF-SOz-CFX wherein X is F or CF;, contained inan inert organic solvent and obtaining as a result thereof a compound ofthe formula CF =CFOCF CFXSO Me wherein X has the same meaning asindicated above and Me is the alkali metal of the alkoxide.

References Cited UNITED STATES PATENTS 3,301,893 1/1967 Putnam et a].3,402,197 9/1968 Nychka. 3,282,875 11/1966 Connolly et al.

DANIEL D. HORWITZ, Primary Examiner US. Cl. X.R.

